import 'dart:async';
import 'dart:convert';
import 'dart:math' as math;

import 'package:http/http.dart' as http;
import 'package:latlong2/latlong.dart';
import 'package:rra_app/pages/map/constants.dart';

class BusStop {
  const BusStop({
    required this.id,
    required this.name,
    required this.position,
    this.stopLetter,
    this.towards,
  });

  final String id;
  final String name;
  final LatLng position;

  final String? stopLetter;
  final String? towards;
}

class TflBusStopService {
  TflBusStopService();

  // streams bus stops — emits once from cache, then again from TfL if fresher
  Stream<List<BusStop>> fetchInRect(LatLng sw, LatLng ne) async* {
    final uri = Uri.parse(
      '$kBackendBaseUrl/stops'
      '?minLat=${sw.latitude}'
      '&minLon=${sw.longitude}'
      '&maxLat=${ne.latitude}'
      '&maxLon=${ne.longitude}',
    );

    final client = http.Client();
    try {
      final request = http.Request('GET', uri);
      final streamed = await client.send(request);

      final buffer = StringBuffer();

      await for (final chunk in streamed.stream.transform(utf8.decoder)) {
        buffer.write(chunk);
        final text = buffer.toString();

        // SSE events are delimited by \n\n
        int idx;
        var remaining = text;
        while ((idx = remaining.indexOf('\n\n')) != -1) {
          final event = remaining.substring(0, idx).trim();
          remaining = remaining.substring(idx + 2);

          if (event.startsWith('data: ')) {
            final json = event.substring(6);
            final stops = _parseStops(json);
            if (stops != null) yield stops;
          }
        }

        buffer.clear();
        buffer.write(remaining);
      }
    } finally {
      client.close();
    }
  }

  static List<BusStop>? _parseStops(String json) {
    try {
      final body = jsonDecode(json) as Map<String, dynamic>;
      final stopPoints = body['stopPoints'];
      if (stopPoints is! List) return null;

      final stops = <BusStop>[];
      for (final raw in stopPoints) {
        if (raw is! Map<String, dynamic>) continue;
        final lat = (raw['lat'] as num?)?.toDouble();
        final lon = (raw['lon'] as num?)?.toDouble();
        if (lat == null || lon == null) continue;

        String? towards;
        final addInfo = raw['additionalProperties'];
        if (addInfo is List) {
          for (final prop in addInfo) {
            if (prop is Map && prop['key'] == 'Towards') {
              towards = prop['value'] as String?;
              break;
            }
          }
        }

        stops.add(BusStop(
          id: raw['id'] as String? ?? '',
          name: raw['commonName'] as String? ?? '',
          position: LatLng(lat, lon),
          stopLetter: raw['stopLetter'] as String?,
          towards: towards,
        ));
      }
      return stops;
    } catch (_) {
      return null;
    }
  }

  static double metersPerPixel(double lat, double zoom) {
    const earthCircumference = 40075016.686;
    final latRad = lat * math.pi / 180.0;
    return (earthCircumference * math.cos(latRad)) /
        (256 * math.pow(2, zoom));
  }
}